/*
 * Copyright 2011-2012 by The Regents of the University of California Licensed
 * under the Apache License, Version 2.0 (the "License"); you may not use this
 * file except in compliance with the License. you may obtain a copy of the
 * License from
 * 
 * http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations under
 * the License.
 */
package edu.ucsd.db.bassarisk.query.expression.visitor;

import java.util.List;

import edu.ucsd.db.bassarisk.exception.VisitorException;
import edu.ucsd.db.bassarisk.query.expression.Expressions.Expression;
import edu.ucsd.db.bassarisk.query.expression.Expressions.KeywordMatchExpr;
import edu.ucsd.db.bassarisk.query.expression.Expressions.NonterminalExpr;

/**
 * Simplifies declaration of a visitor that collects a certain type of object as
 * it traverses the expression tree.
 * 
 * @param <T>
 *          The type of the objects collected from the expression tree.
 */
public class ExpressionTreeCollectionTraversal<T> extends
    SupertypeDeferingExpressionTreeVisitor<Void, List<T>> {
  @Override
  public Void visitKeywordMatchExpr(final KeywordMatchExpr expr, final List<T> arg)
      throws VisitorException {
    return null;
  }

  @Override
  public Void visitNonterminalExpr(final NonterminalExpr expr, final List<T> arg)
      throws VisitorException {
    for (Expression subExpr : expr.getSubExprs()) {
      subExpr.accept(this, arg);
    }
    return null;
  }
}